(1) Field of the Invention
The present invention relates to a mold for molding a tire. More particularly, the present invention relates to a mold for molding a tire to prevent spew (whisker projections) and burred extensions on a tire surface during tire molding, to allow the retention of the initial performance of a tire obtained and good external appearance, and to allow designing for reduction in the number of molds and their production costs as well as simplification of maintenance and inspection work.
(2) Related Art Statement
The molds for molding a tire are often manufactured by means of casting which fits for the forming of complicated shapes conforming to the surface shape designed as complicated shapes having numerous thin projections termed sharp corners or blades for a tire.
Molds for molding a tire manufactured by means of this casting are ordinarily divided into sub-molds, and these sub-molds are combined to form a predetermined form as a whole at the time of forming a tire. As a method for dividing the mold, a method for dividing into 7-11 sub-molds by cutting the predesigned form in the direction of the central axis along the circumference which are often called segmented molds (or sectional molds), and a method for dividing into 2 sub-molds by cutting the predesigned form in a direction perpendicular to the central axis, that is, in the direction of the tire diameter which are often called 2-piece molds (or One Cast Ring molds). Appropriate selection can be made in accordance with manufacturing conditions and the like.
Molding of a tire using this type of the mold is ordinarily performed by pressing a green tire, which has not been applied with a predetermined design and produced by pre-molding polymerized rubber materials and the like, to a mold. This type of the molding is called as compression molding.
In the course of such a compression molding, a number of closed spaces, which are called blockade spaces, are formed between the green tire and the projections and depressions such as ribs, blades, and the like formed on the mold surface, when a green tire is pressed into a mold. During molding, air within the blockades is not discharged therefrom, and thus, air bubbles are contained in the molded tire finally obtained. This is a problem when air bubble defects, such as air inclusions, are produced.
Further, after molding, molds for molding a tire should be ordinarily subjected to inspection and maintenance treatment, including periodic cleanings and the like, since the surface of the mold is roughened due to adherence of oils and fats and the like during repeated use. Depending on the mold, this cleaning and the like can become troublesome, requiring the introduction of long cleaning times and expensive equipment. This results in a problem that production costs of the articles produced increase.
To prevent the formation of the aforementioned air inclusions, methods of removing air from molds are usually implemented to cope with this situation.
As a means for removing air from the closed spaces, there have been conventionally employed two types of means; one of which is called a venthole type means and the other a non-spew or slit vent type means.
The method employing the venthole type means is such a one that air within blockades is discharged therefrom to the outside through air removal apertures called ventholes provided in the mold so as to make them lead to blockades. In the case of this method, the manufacturing costs of the mold are less expensive and this method has an advantage since one may employ, for maintenance and inspection, a simple blast method which comprises blowing media such as glass beads, resin beads, dry ice pellets, and the like to the interior surface of the mold with high-pressure air. However, spew (whisker projections) are formed on the final molded tire (the tire product) since air is discharged accompanying the outflow of raw tire material (a green tire) into ventholes when the venthole type means is used. There is a disadvantage in that the external appearance and initial running performance of the molded tire are deteriorated.
The method employing a non-spew or slit vent type means is such a method that air within blockades is discharged to the outside through gaps formed between sub-molds or slit-like air removal means provided in the predetermined locations; thus this method is superior in the external appearance with respect to a molded tire. Further, there is an advantage in that adverse effects on the initial running performance are not seen. The occurrence of spew can be prevented when a non-spew or slit vent type means is employed, however, it cannot prevent the formation of burred extensions. Further, in the case of this type of a mold, not only is the production cost of a mold expensive, but also there is a disadvantage in that clogging during molding occurs readily in addition to being more expensive. In addition to the above, with regard to maintenance and inspection, the mold should be broken down into every sub-mold if one employs a simple blast method. Thus, it requires several man-hours for cleaning by blasting. Further, since slit portions clog readily with repeated blasting and the contaminants accumulated in slit portions are difficult to remove, special cleaning methods such as chemical cleaning and plasma cleaning should be used. This requires long cleaning times and the introduction of expensive equipment. This is a disadvantage in that the production costs of the molded item increase.
As mentioned above, there are respective advantages and disadvantages in these two type means for air removal. Therefore, at present, one should choose a proper mold taking into consideration the use of tire to be produced, production costs, and the like. That is, at present, a mold equipped with a non-spew type means is used when a serious consideration must be given to the external appearance and the initial performance of a tire, with the acceptance of a relatively expensive production cost. On the other hand, however, a mold equipped with a venthole type means is used when a serious consideration must be given to the production costs of a mold and the running costs in tire molding, with the acceptance of a relatively poor external appearance and relatively poor initial running performance of a tire. Thus, a satisfactory balance between all aspects of the external appearance, the initial performance and the production costs of tire is desired.
In light of these circumstances, various types of measures are being proposed. For example, there is proposed in JP-A-9-141660 a mold equipped with air removal lids provided in ventholes. This air removal lid is provided with a movable lid insert comprising an axis and a lid head disposed thereon. This lid head is provided with a cavity and a surface having a circular-truncated-cone-shape on the opposite side of the cavity, and being mostly flat on the side near to the cavity. Further, this air removal lid is provided with a casing and is press fitted into the venthole together with this casing.
An air removal lid thus configured has the functions mentioned below. Namely, the lid insert is always pressed to upper side by means of a spring loaded with force. Moreover, the lid insert is, during compression molding using a green tire, pressed down in opposition to the loaded force of a spring by means of pressing a level surface of the lid head into a green tire. During this downward pressing, air can be removed through gaps, that is, air passages, formed between the casing and lid insert. Further, infiltration into air passages of the green tire can be prevented by interrupting air passages with such contact of the casing and the circular-truncated-cone-shaped surface when compression molding is completed. Furthermore, the lid insert is pushed upwardly again by means of a loaded spring in the cavity during removal of the vulcanized tire from the mold after vulcanization is completed.
Nonetheless, a mold provided with the air removal lid suffers, as mentioned later, from clogging in a relatively high frequency due to constraints of that structure. The xe2x80x9cleakage distance,xe2x80x9d which is an index for judging the easiness in clogging, is defined as xe2x80x9cArea in the Opening and Closing Surface of an Air Removal Lid,xe2x80x9d and also as the contact area between the casing and the circular-truncated-cone-shaped surface in the case of the device disclosed in JP-A-9-141660, or, in other words, the xe2x80x9cdistance from the peripheral portion of the lid opening and closing surface to the holes for air removalxe2x80x9d and the distance from the peripheral portion of the casing to the entrance of air passages in the case of the device disclosed in JP-A-9-141660 cannot be set to be long. In this event, rubber burrs are readily reachable up to the air removal holes, i.e., air passages during tire molding. As a consequence, there is such a problem that they infiltrate into air removal holes and cause clogging. Namely, the constraints are present as a result of the structure since the air removal lid must be embedded inside a tubular casing and stored. To avoid interference in designing, one cannot employ a casing having an external diameter in terms of radius of approximately 3 mm or more. In this event, the internal diameter of the casing should be shortened to have a long leakage distance. The radius, however, must be approximately 1.6 mm even at a minimum since the air removal lid is housed in the venthole. Therefore, since there exists the boundary in having a long this leakage distance, clogging occurs readily from rubber burr infiltration into air removal holes (air passages). Thus, this brings a problem that the increase in the maintenance expenses (running cost) cannot be eliminated. Moreover, in the case that rubber burrs which have been temporarily infiltrated into the internal area of the air removal holes (air passages) are cut off at the time of demolding the tire from the mold, this would result in a further rise in the probability of the occurrence of clogging. This is because a portion corresponding to the leakage distance is housed in the internal portion of the air removal holes (air passages). Further, there is a problem in that production costs increase due to the numerous parts and complicated structures.
It is an object of the present invention, in light of the above problems, to provide a mold for molding a tire so that when molding a tire, the occurrence of spew (whisker projections) and burred extensions on a tire surface is prevented and the tire obtained can have good initial performance and external appearance, at the same time, reducing the number of the sub-molds in the mold and their production costs and effectively preventing clogging derived from rubber burr infiltration in ventholes and for allowing design to reduce running costs by simplifying maintenance and inspection work.
Accordingly, there is provided a mold for tire molding described below in detail.
According to one aspect of the present invention, there is provided a mold for molding a tire, comprising: at least two sub-molds being capable of forming a predetermined form as a whole when used for molding a tire, characterized in that the mold is equipped with the at least two sub-molds, each of which has a plurality of air removal apertures for discharging air from blockades formed between a green tire and sub-molds when the green tire is pressed on respective surfaces of the sub-molds during tire molding, and a plurality of ventlids, each of which has a lid mechanism. The lid mechanism is made of a flexible, and chemically inactive material without fusing with the green tire, and being capable of using repeatedly at a temperature of 100-200xc2x0 C., discharging air from blockades with keeping an open state by spring up until the green tire contacts an upper portion of the mold when the green tire is pressed on respective surfaces of the sub-molds during tire molding, continuing to discharge air while reducing degree of its spring up during a period from a time when the green tire contacts the upper portion to a time when it reaches the surface of the sub-molds, and preventing the green tire from flowing out of the ventlids by forming a closed state where the ventlids are intimately contact with the green tire by dissolving its springing up when the green tire reaches the surfaces of the sub-molds.
According to a second aspect of the present invention, there is provided a mold for molding a tire according to the first aspect, wherein the ventlid is a flexible plate member and the lid mechanism of the ventlid passes through the direction of the thickness of the ventlid; the ventlid being formed by bending upwardly at a predetermined angle a cut portion cut along with a baseline formed by a straight line linking a starting point and an end point both of which are a starting point(s) and an end point(s) of one or more straight or curved cuts, and do not coincide each other.
According to a third aspect of the present invention, any one of the molds of the first and second aspects is provided, wherein the lid mechanism formed inside the venthole or formed as a venthole itself is provided with means of positioning to prevent further pressing downwards when there is formed a closed state where the ventlids are in intimate contact with the green tire by dissolving its springing up at a time when the green time reaches the surfaces of the sub-molds.
Fourthly, there is provided a mold according to the third aspect of the present invention, wherein the means of positioning is a positioning pin disposed in a standing form in direction of the central axis of the venthole so as to make an upper portion thereof contact intimately with the lid mechanism in a closed state by means of a support member provided in the venthole.
Fifthly, there is provided a mold according to the third or fourth aspect of the present invention, wherein the means of positioning is a positioning structure where the diameter of the venthole is set to be small so as to make the leading edge of the lid mechanism contact with the upper portion of the peripheral wall of the venthole when the lid mechanism is in a closed state.
According to a sixth aspect of the present invention, there is provided a mold according to the first aspect of the present invention, wherein the ventlid is a flexible plate member, and is formed by bending at a predetermined angle cut portions which are a cut along with a baseline formed one or more continuous or non-continuous straight or curved lines.
Seventhly, there is provided a mold according to the sixth aspect of the present invention, wherein the ventlid is fixed in a vent tube at a weld site by using as a boundary the cuts formed by passing through the direction of the thickness, and the vent tube where the ventlid is fixed is provided in the venthole.
Eighthly, there is provided a mold according to the sixth aspect of the present invention, wherein the ventlid is directly fixed in a predetermined location of the sub-molds a weld site by using as a boundary the cuts formed by passing through the direction of the thickness.
According to a ninth aspect of the present invention, there is provided a mold according to the first aspect of the present invention, wherein the ventlid is a lens-shaped flexible plate member where two circles or ellipses lay in a line and the lid mechanism of the ventlid is formed by bending at a predetermined angle with a baseline of a joint portion where the two aforementioned circles lay in a line.
Tenthly, there is provided a mold according to the ninth aspect of the present invention, wherein the ventlid is fixed in a vent tube at a predetermined location of one plate member of the plate members that are bent; the vent tube where the ventlid is fixed being provided in the venthole.
Eleventhly, there is provided a mold according to the ninth aspect of the present invention, wherein the ventlid is directly fixed by fixing one plate member among the bent plate members at its predetermined location to a predetermined location of the sub-molds.
According to a twelfth aspect of the present invention, there is provided a mold according to the first aspect of the present invention, wherein the ventlid is a keyhole-shaped flexible plate member where a circle, ellipsis, or shell-shape and a rectangular shape lay in a line and the lid mechanism of the ventlid is formed by bending the flexible plate at a predetermined angle by using a baseline a line formed by the circle, ellipsis, or shell-shape and a rectangular shape or a straight line positioned at the proximity of the aforementioned line.
Thirteenthly, there is provided a mold according to the twelfth aspect of the present invention, wherein the ventlid is fixed by embedding directly the rectangular plate member among the bent plate members into a predetermined location of the sub-molds to fix.
Fourteenthly, there is provided a mold according to the twelfth aspect of the present invention, wherein the ventlid is fixed by fixing the rectangular plate member among the bent plate members at its predetermined location to sipe blades disposed in predetermined locations of the sub-molds.
According to a fifteenth aspect of the present invention, there is provided a mold according to the first aspect of the present invention, wherein the ventlid is made of a flexible plate member whose shape is composed of a shape corresponding to design of a shape of the periphery of a tire and a rectangular shape in series, and the lid mechanism of the ventlid is formed by bending the flexible plate at a predetermined angle using as a baseline a portion where the design of the shape of the periphery of a tire and a rectangular shape lay in a line.
According to a sixteenth aspect of the present invention, there is provided a mold according to the fifteenth aspect of the present invention, wherein the ventlid is fixed to a vent tube at a predetermined location of the rectangular plate member among the bent plate members, and the vent tube to which the ventlid is fixed is housed in the venthole.
According to a seventeenth aspect of the present invention, there is provided a mold according to the fifteenth aspect of the present invention, wherein the ventlid is a ventlid in which a predetermined location of the rectangular plate member among the bent plate members is directly fixed in a predetermined location of the sub-molds.
According to an eighteenth aspect of the present invention, there is provided a mold according to any one of the sixth through sixteenth aspects of the present invention, wherein a plate member capable of opening and closing among the bent plate members is made of a plate member having a surface shape corresponding to the surface shape of the sub-molds.
According to a nineteenth aspect of the present invention, there is provided a mold according to the eighteenth aspect of the present invention, wherein a plate member capable of opening and closing among the bent plate members is a plate member to which a shaped component having a surface shape corresponding to the surface shape of the sub-molds is fixed.
Twentiethly, there is provided a mold according to any of the other nineteen aspects of the present invention, wherein the ventlid is made of a silicone elastomer or a fluorocarbon elastomer.